The present invention relates to the field of transmission meters and methods for measuring the transmittance of fluids. More specifically, the present invention relates to a transmission meter and method for measuring the transmittance of a fluid, such as water, in a sterilisation or disinfection apparatus.
Ultraviolet (UV) disinfection equipment works by irradiating the fluid to be purified, with radiation having wavelengths predominantly in the range from 240 to 280 nm. Such UV disinfection equipment has many uses such as treating the domestic and public water supplies, water supplies for the process industry, sewage effluent, and any applications where the presence of pathogens may be injurious to health. Therefore, satisfactory disinfection must be achieved in order to safeguard the health of the public.
To achieve satisfactory disinfection of the liquid, it is important to know the rate of fluid flow, the UV intensity within the disinfection chamber and the fluid transmittance at the wavelength of the UV radiation. Knowing the above will allow the performance of the disinfection equipment to be continuously monitored, and, if necessary, corrective action can be taken if the levels fall below predefined limits.
The flow rate can be easily measured by well known techniques. The UV intensity within the disinfection or purification chamber can also be measured by placing a UV sensor in the chamber. The transmittance of a fluid is generally measured by placing a radiation source in the fluid to be measured and measuring the intensity of the detected radiation at a point distant from the source. The transmittance can be easily calculated if the power of the source, the distance of the detector from the source is known and that there is no other obstruction between the source and the detector.
The problem arises when the sensor is required to monitor the transmittance of a continuously or intermittently flowing fluid over a long time, for example, a few days, weeks, months, even years. A single UV sensor will be able to sense a decrease in the intensity of the light from the UV source over time. However, it will not be able to establish if this is due to the output of the source decreasing over time or, the transmittance of the fluid itself changing. Another factor which will affect the measured intensity is so-called photochemical fouling which occurs due to the fluid depositing particles, especially iron and manganese compounds, on the source and optic surfaces of the sensor.
Previous attempts to address the above problems have included a meter with a detector which is moveable between two positions as described in NL1003961 and a meter with two fixed detectors at different distances from the source as described in JP 10057.
A first aspect of the present invention provides a transmission meter for measuring the transmittance of a fluid, the meter comprising:
a chamber for the flow of fluid therethrough and adapted to receive
an electromagnetic source within said chamber; and
three sensors each configured to measure the output from said source,
wherein each of the three sensors are located at different distances from the source.
The three sensors allow detection of the intensity of the emitted radiation at three different points. The intensity detected at each of the sensors will be dependent on the irradiance of the source, the transmittance of the fluid, the distance of the source from the sensor and the extent of deposition on the optic surfaces of the apparatus. As the distance of each of the sensors from the source is known, it is possible to establish the transmittance of the fluid. More than three sensors could be used if required.
Preferably, the sensors all measure the irradiance from the same part of the source. This eliminates errors due to the irradiance of the source varying across its output surface and variations in photochemical fouling of the source. To obtain accurate readings, it is preferable if the sensors are at significantly different distances from the source. For example, preferably, the distances of the two sensors which are furthest from the source are substantially integral multiples of the distance of the closest sensor to the source.
As previously mentioned, the meter is primarily intended for use in a disinfection apparatus. Therefore, in a second aspect, the present invention provides a disinfection apparatus comprising a transmission meter and a purification chamber, said purification chamber being capable of receiving an electromagnetic source for purifying fluid passing through said purification chamber, said meter comprising an analysis chamber for passage of the fluid therethrough, means for receiving an electromagnetic source within said analysis chamber and three sensors each configured to measure the output from said source within the analysis chamber, wherein each of the three sensors are located at different distances from the source.
Preferably, the transmission meter is located upstream from the purification chamber. Thus, it is used to measure the transmittance of the fluid prior to treatment. This can be achieved by directing a fraction of the fluid in the inlet pipe to the purification chamber into the transmission meter.
In many instances, there will be more than one purification chamber. The plurality of purification chambers will preferably be provided in a parallel arrangement as opposed to a series arrangement.
The data collected by the three sensors in the analysis chamber can be analysed remote from the meter. For example, the sensors could each have means to transmit the data from the meter to a remote analyser, or, the meter could be provided with data storage means for periodic collection by a computer via a hardwire or wireless link or even manually by an operator.
Alternatively, the meter may comprise analysis means to compare the output of the three sensors. The analysis means could output an electrical signal which is related to the transmittance of the fluid. This electrical signal could either be analogue or digital in character.
Preferably, the meter or the disinfection system comprises a controller into which the output from the analysis means is fed. The controller may be used to control the meter to perform calibration or self cleaning functions. Alternatively, the controller may be used to adjust the parameters of the purification chamber to maintain treatment levels within acceptable limits. Typically, there is a predefined minimum level for the treatment level of the chamber.
For example, the controller could be used to increase the power supplied to the radiation source or sources within the purification chamber. In the case where there are many purification chambers provided in parallel, the controller can be used to bring on line or switch fluid away from one or more of the chambers i.e. it can be used to control the number of chambers in use at any one time.
The knowledge of the transmittance of the fluid allows the level of treatment required by the fluid to be accurately computed.
To perform the cleaning and/or calibration functions, the meter preferably further comprises valve means configured to switch the supply of fluid into the chamber between at least two different sources. The two sources are preferably a source containing the fluid which is to be measured and a source containing de-ionised water which has virtually 100% transmission at UV wavelengths. UV wavelengths are typically between 200 nm and 400 nm, and more specifically from 240 nm to 280 nm.
More preferably, the meter further comprises at least one valve which is capable of switching between three sources. The sources are preferably, the fluid which is to be treated, a de-ionised water source and a source of weak acid. The weak acid supply is used to clean the chamber. The weak acid may be a dilute phosphoric acid, for example, a solution containing about 5% phosphoric acid by volume, or it could be another acid for example hydrochloric acid at a similar strength. The valve means could also be configured to switch the supply between just untreated fluid and weak acid.
Preferably, the source chosen by the valve means is controlled by the control means.
Providing the transmission meter with an inlet which can be switched between two or more supplies allows the transmission meter to be cleaned, calibrated etc without the need to disassemble the system. Therefore, in a third aspect, the present invention provides a meter for measuring a fluid, the meter comprising a chamber for the passage of fluid therethrough, at least one sensor for detecting a parameter within the chamber and means for switching the type of fluid which flows through the chamber dependent on the parameter detected by at least one sensor.
The sensed parameter can be the fluid transmittance, the irradiation from a radiation source located within the chamber etc. The different types of fluid may be chosen from the fluid which is to be measured in the chamber, a reference fluid, (for example, pure water), which can be used to calibrate the system or a cleaning fluid (for example, an acid). The meter can be used to measure any property of the fluid, for example, the transmittance, flow rate etc.
Preferably, the purification chamber also comprises cleaning means for cleaning the chamber. These cleaning means may be provided by a mechanical system which operates on a fixed time cycle. These cleaning means may be controlled by software which is used to detect when the UV level within the chamber falls below a certain limit. These cleaning means may also be controlled by the control means.
Preferably, the apparatus further comprises a flow meter such that the rate of fluid flow through the purification chamber and the transmission meter can be monitored.
Above, the disinfection apparatus has been described as having two chambers, an analysis chamber and a purification chamber. However, the analysis of the transmittance of the fluid under treatment could be performed within the purification chamber.
Therefore, in a fourth aspect the present invention provides a disinfection apparatus comprising a purification chamber adapted to receive an electromagnetic source for purifying liquid passed through said purification chamber, the apparatus further comprising three sensors each configured to measure the output from said source, wherein each of the three sensors are located at different distances from the source.
Typically, the purification chamber will have a plurality of sources. Preferably, to obtain consistent results, the three sensors will measure the output from the same electromagnetic source. Even more preferably, from the same part of the source.
In a fifth aspect, the present invention provides a method for measuring the transmittance of a fluid, the method comprising the steps of:
passing the fluid between an electromagnetic source and three sensors configured to measure the output from said source, wherein each of the sensors are located at different distances from said source; and
measuring the output of the source using each of the three sensors.
The present invention will now be described with reference to the following preferred non-limiting embodiments.